In recent years a great deal of interest has been shown in the provision of electrochromic displays having, for example, a digital or analog readout such as in copending commonly assigned U.S. patent application Ser. No. 547,277 filed Feb. 13, 1975 in the name of Leo Wiesner.
Typically, the driving circuit for or method of changing the information being displayed consisted of the two visually distinct operations of consecutively and separately writing and erasing the selected segments to effect the change, such as in U.S. Pat. Nos. 3,807,832 issued Apr. 30, 1974 to George Augustus Castellion and 3,839,857 issued Oct. 8, 1974 to Donald Joseph Berets and George Augustus Castellion.
Thus, from the prior art, it is known to separately write selected segments by applying a voltage V.sub.1 of one polarity (usually negative) with respect to a common electrode for a period to completely write the selected segments and then, consecutively, to erase a segment by separately applying a voltage V.sub.2 of opposite polarity with respect to the same common electrode for a period to completely erase the selected segments. It is also known to write and erase only those segments requiring change, when changing or updating the character to be displayed, and to utilize the inherent memory of the display by not switching those segments required to remain in their respective "on" or "off" states.